at that time, khan's death was determined to be from natural causes. but a few days later, the medical examiner says a relative of khan called to suggest there may be more to the story. more tests were done, and cyanide was found in his blood. >> you know, once we found that it was qualitatively present, clearly that raises flags, because it shouldn't be detected at all. so once that was in the mix, i wasn't that surprised that eventually we had a lethal level. it doesn't take that all much cyanide to kill a person. >> and now chicago police are investigating it as a murder. >> if you're going to try to commit the perfect murder, this is a good way to do it. >> reporter: lawrence kobilinsky is a professor of forensic science. he says cyanide is not easily detected on drug screenings and a small amount can kill a person quickly. and he said, labs are only one place to find it. >> it's usually kept under lock and key, but, again, if you work in the photographic industry, if you worked in a metal processing plant, electroplating, for example, or if you wo